St. Anthony Falls Historic Cutoff Wall: Preliminary Risk Assessment
A state funded investigation into the present-day condition of the 1876 cut-off wall and other historic subsurface structures.
Project Overview
During the 2023 Minnesota legislative session, the Minnesota state government requested that the University of Minnesota assemble a project team to assess the Upper St. Anthony Falls cutoff wall and surrounding surface and subsurface infrastructure. The state allocated funds to complete this assessment by June 2025. This two-year study will evaluate the current condition of historic subsurface structures (cutoff wall and tunnels) located at the Upper St. Anthony Falls. We seek to assess the potential risk for structural, geotechnical, or hydraulic failures at the site and what the consequence of failure would be to existing civil infrastructure.
Activity 1: Uncovering the history of the cut-off wall construction
The project will dig into historic documents, journals, maps, and other archival information to learn about events that led to the Eastman Tunnel collapse, the mitigations attempted to respond to the collapse, and the constructi0n of the cutoff wall.
Activity 2: Field surveys of present-day condition of the cutoff wall
The project will carry out non-destructive surveys of the cutoff wall and surrounding bedrock using advanced geophysical techniques, land surveys, and inspections. This is an especially important task that will provide new insights into the condition of the cutoff wall, the possible existence of voids in sandstones and or stability of structures built in the 1800's to stabilize and block the Eastman Tunnel.
Survey work will occur during calendar year 2024.
Activity 3: Physical modeling failure scenarios at St. Anthony Falls
A reduced-scale physical model will be constructed of the Upper St. Anthony Falls region and will include the cutoff wall and subsurface tunnels. The model will be used to explore the Eastman Tunnel collapse and also used to examine possible failure scenarios and how these failures would impact the region. The model will be constructed at the University of Minnesota, St. Anthony Falls Laboratory.
Modeling will occur in 2024 and 2025.
Activity 4: Risk assessment of civil, life-safety, and economic impacts
Led by Hennepin County Emergency Management, this activity will review important civil infrastructure around the Upper St. Anthony Falls as well as upstream and downstream of the site. The team will evaluate how various failure scenarios of the cutoff wall would impact the region. Assessing probability of failures, response time needed for certain failures, and mitigation planning are all part of this activity.